Transformers-Energy conservation

Discussion in 'General Electronics Chat' started by uzair, Jan 23, 2008.

  1. uzair

    Thread Starter Active Member

    Dec 26, 2007
    110
    0
    In a transformer (step-up specifically), how is energy conserved?

    If someone can give a neat statement about law of conservation of energy for transformers, it would be of great help!!
     
  2. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    transformers whether step up or step down have nothing to with energy.
    they only step up/down the emf.
    of course there are losses in transformer...loss due to eddy currents...hysteresis...in core.
    loss due to heat dissipated across the windings.

    ABOUT ENERGY:what consumes energy are the components powered by transformer's secondary...this power is supplied by the source connected to primary....this also takes care of losses in a transformer.

    any load connected across HV side is seen by primary as of a smaller resistance(divided by square of transformation ratio) and hence the current thru primary(LV) is larger...but for secondary the current is smaller..thus the product of V*I for both side is same...thus power=V*I remains constant..
    it is better to talk in terms of power IMHO when dealing with anything electrical since it involves current ..which itself is a time rate of charge flow.
     
  3. uzair

    Thread Starter Active Member

    Dec 26, 2007
    110
    0
    Consider that a smaller emf source is connected to a primary coil and the secondary coil steps up this emf and delivers power to the load.Actually i am confused that if we had connected that load to the emf source (originally attached to primary) separately then it would have delivered less power.
    What do you say about it?
     
  4. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    yes(if it is some kind of bulb or so), but the power required wud have been delivered by the source..not the transformer...lets say(for the sake of simplicity lets forget an alternator)..some sort of battery was providing power to the load..since now power is high(resistance of load remaining same)the battery will now discharge less quickly.in case of alternator..the torque to primemover will now be less and now less work will be required from primemover.
    if it were a motor it wud adjust current accordingly for the required power.and power wud be same with or without step down.

    this might explain better.
    ..its just that when the load is connected on secondary, the resistance of load to the primary(of the voltage level of source)seems much smaller(by a factor of step up ratio squared!!!!) and consequently larger current now flows..for the same voltage.in primary..giving much larger power consumption..its just like reducing the resistance of the bulb(load)..for same voltage..the power for this will still be required to be provided by the turbine/primemover..else its gameover, in this case the generator speed will fall down..leading to lesser voltage at o/p..till VxI matches the power to the generator rotor....talking in terms of energy...u might have to increase power to generator..and ur energy source will be exhausted at higher rate...its not transformers fault...its ur fault ..u demanded faster rate of energy consumption...if u use XF as step down...u are asking for a lesser rate of energy consumption.
     
  5. uzair

    Thread Starter Active Member

    Dec 26, 2007
    110
    0
    Thanks for the reply.The concept is much clear now.
     
Loading...